Selecting circuit



Oct. 2s, 1941. M. P. WILDER SELECTING CIRCUIT `Filed May 6, 1938 R l E o@n o m w w n w ww M mv@ um @I .nv m W L .l mm w mm N L A Mm@ BMI, I l.,mwwwmw Nm nflm lmm im Jl @m A Y u AB o@ mm M C Imm $25251. JllLunas-3223 NN Q T AAAAAAAAAAAAIAAAAAIAAAAAAAI Patented Oct. 28, 1941UNITED STATES PATENT o FFICE 2,260,963 sELEcTING CIRCUIT y Marshall P.Wilder, Maplewood, J. z 1 ApplicationM'ay 6, isssrsevrsial No. 206,325

8 Claims.

The invention relates to a separation or selection circuit and isespecially applicable for use with a television receiver for the purposeof separating or selecting a synchronizing signal or signals from thecomplex signal which includes the synchronizing blanking and picturesignal. Selectors in general employ a ymeans for separating one portion'of a given complex signal, having a plurality of portions of differentvoltage amplitudes, from another portion of that signal by properlybiasing a detector so that signals ofan amplitude, either greater orless than that desired,rwill not pass through the detector, but thedesired signal does pass therethrough. .k` An object of the invention isto produce a new and novel ycircuit for selecting synchronizing signalsto control sweep circuits of television receivers which will separatethe video signal and the synchronizing signal and also separate thesynchronizing signal into its line and field synchronizing signals.

Another object of the invention is toA producev aselecting circuit whichutilizes an amplitude selector and a circuit having a time constant suchthat a predetermined frequency or amplitude of signal applied theretowill cause no building up of voltage therein, but a signal having afrequency or amplitude greater than the predetermined frequency oramplitude will cause an increase or building up of voltage in thiscircuit which controls a iiow of current through the amplitude selector.l

Another object is to devise a synchronizing circuit which will functionto separate ak compound signal into its parts irrespective of whetherthe signals differ as to amplitude or frequency. Y

A further object of this invention is to provide a means, simple andreliable, which will allow accurate phasing of an interlaced pattern tobe reproduced in its original phase relation in the output circuit ofthe amplitude and frequency selector.

Other objects of the invention will be more `apparent from thefollowingdescription taken in connection with the accompanying drawing,illustrating preferred embodiments of the invention, in which: y v

Figure 1 is a circuit diagram of one simple form of the invention asapplied particularly for a television receiver adapted to receivenegatively modulated signals. 'Ihe circuit illustrated thereforeincludes the final stage of a video amplifier and leads adapted to beconnected with the low frequency and high frequency sweep circuits of atelevision receiver.

Figure 2 shows a circuit diagram as applied particularly for theselection of synchronizing signals for a television receiver adapted toreceive positively modulated signals.Y This diagram also shows a videoamplifier of the'output pentode subject to certain difliculties.

type, and connections which may be made With the low frequency and highfrequency sweep circuits of the television receiver. The essentialdifference between the two circuits is that the diodesare reversed inone figure with respect to the diodes in the other figure. y

The vuse of circuits hitherto forv separating the video signal andthefield and line synchronizing signals from a received television signalhave been One important diiculty was that the characteristic curve ofthe network did not saturate deeply enough and it was diicult todetermine the exact point where cut-out occurred. This diii'iculty inmaintaining independent control of the various functions of a circuitthrough disadvantageous limitations introduces undesirable errors in theprior art frequency and amplitude circuits as they are generallyemployed.

The invention disclosed in Figure 1 takes the negatively modulatedsignal which is amplified in the tube I0 and separates it into itsvarious component parts which, if it is a television signal, comprisesthe video, line and field synchronizing signals which are parts of acombined or complex signal. This tube may be of any desired.

type. The plate of the tube is connected to a source of potentialthrough a wire I I and a resistor I2. IAs an example, for use with atele- Vision receiver, the resistor I2 preferably has a resistance ofabout2000 ohms, or of such value thatthe voltage drop therethrough maybe about 5 0 volts. A wide range of voltages is permissible. A rstamplitude selector I5, which preferably is a diode,A has its anode orplate connected directly with the plate of the tube ID. The cathode ofthe diode is. connected to a source of potential through a timingcircuit which includes a resistance I6 and a condenser Il connected inshunt therewith, an adjustable connection I8, and a The connection IBenables theA resistancer I9. potential upon the cathode of the rst diodeto be adjusted to the proper value, vas will appear morefullyhereinafter. The cathode of the diode I5 is also connected through acondenser 20 and wire 2I to the circuit which will use the impulsepassing through the first diode, such as a high frequency. or line sweepcircuit of a television receiven s n The cathode of thegrsi; amplitudeselector or diode yI5 is connected with the anode or plate of .a secondamplitude selector 24 which also is preferably a diode. s The cathode ofthe diode 24 isconnected with the low frequency or frame s'w'eep of atelevision receiver through a blocking condenser 25 a'ndIwire 26. Thecathode of the diode 24jis connected through a resistance 2l to anadjustable connection 28 which contacts with a resistance 29 Ywhich isconnected with a source of potential'P. The adjustable connection 28enables the potential upon the cathode of the second amplitude selectoror diode to be fixed at its proper value, as will appear hereinafter. Abypass condenser 3] is connected between the variable connection I8 andground G, and a by-pas-s condenser 3I is connected between the variableconnection 28 and ground. The resistance I9 is connected to groundpreferably through a voltage regulator tube 32.

The circuit described above and illustrated in Figure 1 operates in amanner now to be described. Suppose that the voltage of the source ofpotential which is connected with the output tube I is 250 volts and thedropping resistor I2 has a resistance of about 2000 ohms, the plate oranode current drawn through the resistor will cause a voltage drop sothat the potential at the anode will be about 200 volts. or in otherwords, there is a drop of about 50 volts in the anode output resistance.The anode of the first diode I5 is joined directly to the anode of theoutput amplifying tube I0 so that the potential of the former is thesame as and varies with the potential upon the plate of the tube IIJ.Now the voltage on the cathode of the first diode I5 is adjusted by theconnection I8 to a value so that the cathode will be more positive orhave a higher voltage than the anode of 'the diode which may be, say,220 volts. In this condition no current can flow from the cathode to theanode of the first diode.

Now let it be assumed that a negative voltage arrives on the grid of theoutput amplifying tube I0 which causes less current to flow through thetube and resistor and hence will raise the anode voltage from 200 toabout 220, or perhaps a little over. r ihe cathode of the diode I5 is at220 volts so that a voltage condition has been reached between cathodeand plate of the diode which will just begin to allow current to passtherethrough. If the grid of the output tube becomes still more negativebecause of the received signal, this will further increase the voltageon the plate of the output tube as Well as on the plate of the diode tosomething greater than 220 volts, and hence the cathode of this firstdiode will be sufficiently negative with respect to its anode, or theanode will be sufficiently positive with respect to its cathode that acurrent will flow through the first diode and the resistor I6. It willbe seen, therefore, that only that portion of a signal, the amplitude ofwhich is large enough, such as the synchronizing portion of a televisionsignal, will get through this biased detector or first diode.

Now if the frequency of the signal which gets through the first diode I5is of the order of 10,000 cycles and the time constant of the condenserI'I resistor I6 combination is calculated or selected short enough, thecondenser will be completely discharged by the resistor, each time it ischarged up, and the potential on either side of this circuit will remainsubstantially constant.

Now, if either the frequency or the duration of an impulse of the signalwhich passes through diode I5 is greater than that which will dischargethrough the resistor I6, this higher frequency or longer impulseduration will charge the condenser II faster than the resistor I6 candischarge it, and the signal will integrate or build up voltage in thistiming circuit at the point L. In other words, the potential on the sideof the capacity resistance or timing circuit at the junction of the rstdiode I5 and the second diode 24 will increase and hence increase thepotential upon the plate'of the second diode 24.

The cathode of the second diode 24 has its potential adjusted by apotentiometer, that is by the adjustable connection 28, higher than ormore positive than the plate of the second diode so that normally nocurrent will flow therethrough. However, by the integration or buildingup of voltage amplitude in the timing circuit I6, I'I, the plate becomesmore positive than the cathode and a current will then flow through thissecond diode, which current will control the low frequency or fieldsynchronizing sweep of the television receiver.

The timing circuit I6, I'I functions in a wayl which enables the circuitto select the voltage at any point in the process of voltage integrationor at any desired synchronizing signal. It has been described how thetiming circuit builds up or integrates impulses from a signal either ofgreater magnitude or greater duration than the frequency orduration forwhich the timing circuit has been designed to discharge before the nextimpulse is received. This building up of voltage, however, is notuniform, that is would not be a smooth curve if plotted, but one impulseis received and is discharged to a. certain extent and, because of thetiming constant of the circuit, it is not completely discharged ordissipated when a second impulse is received which builds up the voltageto a still higher level, and this charge begins to discharge through theresistor I6, but before it is discharged a third impulse sends thevoltage still higher and so on. The extent of the discharge for eachimpulse, which is, however, relatively unimportant, depends upon thetiming constant of the timing circuit I6, I'I, but by adjusting orsetting the voltage upon the cathode of the diode 24 through theconnection 28, this second diode can be set to pass current therethroughat any desired one of these integrations and hence at any desired'synchronizing impulse. This gives extremely accurate control of the lowfrequency or field sweep circuit.

In some types of synchronizing systems, the synchronizing signal doesnot consist of impulses of different frequency as in one system, butconsists instead of an impulse of greater or longer amplitude thanothers. The circuit described will function in the same manner asdescribed above, and the second biased diode 24 will select this type ofsignal equally as well and with the same accurate control as for asignal of a different frequency, as described above.

The circuit illustrated in Figure 1 may be used for separating orselecting a signal, such as a positively modulated television signal,into its separate parts merely by reversing the connections with thediodes I5 and 24 and proper adjustment of the potentiometers for thediodes. as will be explained hereinafter. Figure 2 shows a circuitessentially like the circuit of Figure l, but with the diodes reversed.A few other changes, which are not essential in order to convert thecircuit of Figure 1 for positively modulated signals, are illustrated.These unessential changes are shown to illustrate some ofthe changeswhich may be made in the circuit without deviating from the invention.In Figure 2 the platev of an output pentode is connected with a sourceof potential P through a resistance 31, preferably a choke 38, and awire 39. The circuit may use a double diode 40, in place of the separatedidodes I5 and 24 illustrated in Figure 1, which functions identicallythe same as a pair of single diodes. The cathode 4I of the first diodeis connected with the-plate of the pentode 36. The plate42 ofthe rstdiode is connected through a condenser- 43 and wire 44 tothe highfrequency or line sweep of a television receiver.

The plate 42 of the first diode is also connected withY the cathode 48of the second diode, and the plate 49vof this second diode is connectedthrough a condenser 50 and wire 5I to the low frequency or field sweepof the television receiver. The plate 42 of the first diode is connectedto a resistance 52 which is shunted by a condenser 53 to form atimingcircuit identical in function with .the timing circuit I6, I'I ofFigure 1. The value of condenser and resistance is determined orselected so that one signal, such as the line impulse of a televisionsignal, will discharge through the resistance before a second lineimpulse is received, but an impulse of greater frequency or duration,such as a eld signal, will not discharge before a second impulse isreceived and hence the potential between .the diodes builds up. Theresistance 52 is connected to an adjustable connection 54. Theadjustable connection may be connected anywhere along the resistance 55to form a potentiometer, and the resistance is connected between thesource of potential P and ground preferably through a voltage regulatortube 56. y The plate 49 of the second diode is connected through theresistance 59 to an adjustable connection 60 which may be connectedanywhere along a resistance 6I to form a potentiometer. A by-passcondenser 62 is connected between the variable connection 60 and theadjustable connection 54, and a second by-pass condenser 63 is connectedbetween the adjustable connection 60 and a wire 64 connected between oneof the grids of the pentode 36 and ,the positive side of the voltageregulator tube 56.

In the construction of Figure 2, the adjustable connection 54 is movedso that the plate 42 of the first amplitude selector or diode becomesmore negative than the cathode 4I, or has a potential lower than thatupon the cathode. If now a signal having a positive potential is appliedto the grid of the output pentode 36, an increased current passesthrough the pentode and resistance 3'I which increases the voltage dropthrough the resistance, so that the cathode 4| becomes more negativethan the plate 42 and a current passes through the diode lto control thehigh frequency or line sweep circuit of the television receiver. Theresistance capacity circuit 52, 53 has been calculated or selected sothat the condenser will discharge through the resistance before a secondimpulse is received and hence no integration occurs.

Now if a positive potential is applied to the grid of the output pentode36 which has a higher frequency or agreater amplitude than can bedischarged by the resistance capacity circuit 52, 53, before a secondimpulse is received, these impulsesintegrate in .the timing circuit 52,53 in the same manner as described in connection with the timing circuitI6, I'I of Figure 1. The potential on the plate 49 of the secondamplitude selector, or second diode, has been set through the adjustableconnection 60 so that the potential normally thereon is more negativethan the potential upon the cathode 48 and current normally does notpass therethrough. The higher frequencyv or greater amplitude signal,however, integrates in the resistor condenser circuit 52, 53 so that thecathode 48 of the second amplitude selector or diode becomes morenegative than the plate 49 and a current passes Itherethrough whichcontrols the low frequency or, field sweep circuit of thetelevisionreceiver.

Itwill be readily understood from the description of the circuit, inconnection with Figure 1, that the potential'upon the plate 49 may beset so that current passes therethrough at any desired integration ofthesignal, as described in connection with the circuit of Figure 1, andthereby the same very accurate control of the sweep circuits may beobtained. This invention is presented to fill aneed for improvements ina selecting circuit. Itis understood that various modifications instructure, as well as changes iny mode of operation, assembly, andmanner of use, may and often do occur to those skilled in the art,especially after benefitting from the teachings of an invention. Hence,it will be understood that this disclosure is illus- .trative ofpreferred means of embodying the invention in useful form by explainingthe construction, operation and advantages thereof.

What is claimed is:

1. A signal separating circuit comprising an amplifier, means to supplysignals tov said amplifier, a single integrating circuit, a rectifyingdevice connected between said amplier and said integrating circuit,means to render said rectifying device operative to pass to theintegrating circuit only those signal outputs from said amplier whoseamplitude departs from a predetermined value in one direction only, aunilateral conducting device connected to said integrating circuit atthe junction of said rectifying device and said integrating circuit,means to render said unilateral conducting device operative to passenergy'from said integrating circuit only When said energy exceeds apredetermined value, terminal means to derive control signals from thesignal output ofsaid rectifying device, and terminal means to deriveother control signals from the energy passed by the unilateralconducting device.

i 2. A signal separating circuit comprising an amplier, means to supplysignals to said amplifier, a single integrating circuit, a rectifyingdevice connected between said amplifier and said integrating circuit,means to render said rectifying device operative to pass to theintegrating circuit vonly those signal outputs from said amplier whoseamplitude exceeds a predetermined value, a unilateral conducting deviceconnected to said integrating circuit at the junction of said rectifyingdevice and said integrating circuit, means to render said unilateralconducting vdevice operative to pass energyA from said integratingcircuit only when said energy exceeds a predetermined value, terminalmeans to derive control signals from the signal outputs of saidrectifying device, and terminal means to derive other control signalsfrom the energy passed by the unilateral conducting device.

3. A signal separating circuit comprising an amplifier, means to supplysignals to said amplier, a single integrating circuit, a rectifyingdevice connected between said amplifier and said integrating circuit,means to render said rectifying device operative to pass to theintegrating circuit only those signal outputs from said amplifier whoseamplitude falls below a predetermined value, a unilateral conductingdevice connected to said integrating circuit at the junction of saidrectifying device and said integrating circuit, means to render saidunilateral conducting device operative to pass energy from saidintegrating circuit only when said energy exceeds a predetermined value,terminal means to derive control signals from the signal outputs of saidrectifying device, and terminal means to derive other control signalsfrom the energy passed by the unilateral conducting device.

4. A circuit for television receivers for separating higher frequency orportions of longer amplitude durations from a signal having a pluralityof different frequencies or amplitude durations comprising a first diodeadapted to be connected in the television circuit and having a cathodeand plate, said first diode being connected with the line controlcircuit of the receiver; a resistance capacity circuit having a timeconstant chosen to allow each pulse of a predetermined frequency andduration to build up a voltage therein and to discharge a portionthereof before the next pulse arrives, the resistance capacity circuitalso having a time constant to discharge for pulses of other frequenciesand durations without an increase of voltage including a resistance, anda capacity connected in parallel therewith, said resistance capacitycircuit being connected to the output of the diode; a second diodehaving a cathode and plate one of which is connected to the input sideof the resistance capacity circuit and the other is adapted to beconnected with the frame control circuit of the receiver; and means toapply a biasing voltage between the cathode and plate of the first diodeby which the cathode normally has a predetermined higher voltage thanthe plate so that current passes therethrough only when the voltage uponthe plate increases over that of the cathode under the influence of asynchronizing impulse, the next aforesaid means also applying a biasingvoltage between the cathode and plate of the second diode by which thecathode normally has a predetermined higher voltage than the plate sothat current passes therethrough only when4 a predetermined number ofthe desired pulses has built up the voltage in the resistance capacitycircuit sufiiciently to bring the plate voltage higher than that of thecathode.

5. A signal separating circuit comprising an amplifier, means to supplya plurality of signals to said amplifier, two of said signals having apolarity opposite to the remaining signals, a single integratingcircuit, a rectifying device connected between said amplifier and saidintegrating circuit, means to render said rectifying device operative topass to the integrating circuit only said two signals from saidamplifier, a unilateral conducting device connected to said integratingcircuit at the junction of said rectifying device and said integratingcircuit, means to render said unilateral conducting device operative topass energy from said integrating circuit only when said energy exceedsa predetermined value, terminal means to derive control signals from thesignals passed by said rectifying device, and terminal means to deriveother control signals from the energy passed by the unilateralconducting device,

6. A s-ignal separating circuit comprising an amplifier, means to supplysignals to said amplifier, a single integrating circuit, a rectifyingdevice connected between said amplified and said integrating circuit,biasing means to render said rectifying device operative to pass to theintegrating circuit only those signal outputs from said amplifier whoseamplitude departs fromv a predetermined value in one direction only, aunilateral conducting device connected to said integrating circuit atthe junction of said rectifying device and said integrating circuit,biasing means to render said unilateral conducting device operative topass energy from said integrating circuit only when said energy -exceedsa predetermined Value, terminal means to derive control signals from thesignal outputs of said rectifying device, and terminal means to deriveother control signals from the energy passed by the unilateralconducting device.

7. A circuit for television receivers for separating higher frequency orportions of longer durations from a signal having a plurality ofdifferent frequencies or durationsI comprising an amplifying tube, aresistance connected in the plate circuit of the amplifying tube, afirst diode connected between the resistance and plate of the amplifyingtube and having a cathode and plate, a resistance capacity circuithaving a time constant chosen to allow certain desired frequencies tobuild up voltages therein and then to discharge a portion thereof, thetime constant also being chosen to discharge for other frequencies ordurations without an increase of voltage including a resistance, and acapacity connected in parallel therewith, said resistance capacitycircuit being connected to the output of the diode; a second diodehaving a cathode and plate one of which is connected to the input sideof the resistance capacity circuit and the other is adapted to beconnected with the frame control circuit of the receiver; and means toapply a bias-ing voltage between the cathode and plate of the firstdiode by which the cathode normally has a predetermined higher voltagethan the plate so that current passes therethrough only when the voltageupon the plate increases over that of the cathode under the influence ofa synchronizing impulse, the next aforesaid means also applying abiasing voltage between the cathode and plate of the second diode bywhich the cathode normally has a predetermined higher Voltage than theplate so that current passes therethrough only when a predeterminednumber of the pulses of the desired frequency and duration has built upthe voltage in the resistance capacity circuit sufficiently to bring theplate voltage higher than that of the cathode.

8. A signal separating circuit comprising an amplifier, means to supplysignals to said amplifier, a single integrating circuit, a firstrectifier connected between said amplifier and said integrating circuit,biasing means to render said rst rectifier operative to pass to theintegrating circuit only those signal outputs from said amplierr whoseamplitude departs from a predetermined value in one direction only, asecond rectifier connected to said integrating circuit at the junctionof said first unilateral conducting device and said integrating circuit,biasing means to render said second rectifier operative to pass energyfrom said integrating circuit only when said energy exceeds apredetermined value, terminal means to derive control signals from thesignal outputs of said first rectifier, and terminal means to deriveother control signals from the energy passed by the second rectifier.

MARSHALL P. WILDER.

